Fuel cells convert chemical energy from fuels such as hydrogen into electricity through a chemical reaction with an oxidizing agent. The cells are generally comprised of three adjacent parts, an anode, an electrolyte and a cathode and two chemical reactions occur at the interfaces of these parts. Generally, as a result of the chemical reactions, fuel is consumed and water and an electric current are created.
It is well known that a plurality of fuel cells may be stacked together in order to increase power output. However, in order to achieve optimal power output, fuel cell stacks are heavily compressed to reduce contact resistance between cell components, thereby reducing the amount of electricity dissipated as heat. In order to fasten a fuel cell stack generally two end plates are used to maintain an optimal contact pressure between the interfaces of the fuel stack assembly. Proper contact pressure is required to both increase energy efficiency by reducing ohmic loss and prevent leakage of fluid. With regard to increasing energy efficiency, it is important to increase the surface area of the fuel cell as much as possible.
Also, fuel cells generally operate at high temperatures which may result in the dimensions thereof changing as the cells become active.
Clamping devices for securing fuel cell stacks under compression are known in the art. Japanese patent no. JP 2012-028194 (to Honda) discloses a fuel cell stack having first and second endplates disposed on either side of the stack. The endplates are clamped by means of a fastening member generally defining a cantilever shape which is inefficient for maintaining axial compression pressure.
Japanese patent no. JP2012-181996 (to Nissan) also teaches of a clamping device for a fuel stack. As with the Honda patent, the clamping device employs a cantilever shape which is inefficient in maintaining compression across the surface area of the fuel cell stack.
Japanese patent no. JP2010-198861 (to Panasonic) describes a cell pressing assembly which uses pre-compressed springs located within a rigid frame to exert pressure on cell elements. The assembly utilizes bolts to secure the spring elements in a compressed state which need to be removed to allow the springs to expand once inserted into the rigid frame. The need to remove the bolt elements renders is time consuming and it is difficult to re-set tension in response to creeping of the stack components in use.